overclocking the cache?

Hi!
I have a PWS433a with 2MB cache. If I set the clockspeed to anything higher
than 433mhz it reports 0MB cache. When I set it back to 433mhz I have the 2MB
cache again. I've tried 500, 533, 566 and 600mhz. It seems to work fine on
all speeds, but without the cache....
Do I have play with some other switch or jumper to make the cache work with
other clockspeeds or am I stuck with 433mhz?
Anyone out there with experience overclocking the Alpha?
Regards
Per Wigren